Friendship books or FB for short are small booklets filled with addresses of people who are into pen palling. They come in any size and shape and it is always big fun to take a look at where it had traveled. They are passed from a person to a person and every single one of them signs in it with his/hers address and additional short information, before pass ing them to the next person (pen pal). The idea behind the Fbs is that the people after you may choose to write to you, or you can choose to write an introduction letter to one of the people/addresses before you.
You can start Fbs for yourself or for friends. They sometimes have little rules: you should make several Fbs for different people, or you have to pass them to people in specific country(s) only. Whatever the rules there, I am sure that you will be soon enjoying yourself. When they are full please be fair and return to owner!